Etymology
Derived from the appearance of irregularly shaped stone paving, known as “crazy paving,” which resembles the radiologic pattern of intersecting linear opacities over ground-glass opacity.
AKA
- None
What is it?
The crazy paving sign is a radiologic finding characterized by ground-glass opacity with superimposed thickened interlobular and intralobular septa, creating a pattern similar to irregular stone paving.
Characterized by
- Ground-glass opacity (GGO) combined with thickened interlobular and intralobular septa.
- The result is a polygonal or reticular pattern resembling a mosaic of irregular paving stones.
- Typically visualized on CT.
Anatomically affecting
- Lung parenchyma, primarily involving the alveoli and interstitium.
Causes include
- Most Common Causes:
- Pulmonary alveolar proteinosis (PAP): Classic association of the crazy paving sign.
- Other Causes include:
- Infection: Pneumocystis jirovecii pneumonia (PJP), viral pneumonia (e.g., COVID-19, influenza).
- Inflammation: Sarcoidosis, nonspecific interstitial pneumonia (NSIP), organizing pneumonia.
- Neoplasm: Bronchoalveolar carcinoma (adenocarcinoma in situ).
- Mechanical: Pulmonary edema.
- Trauma: Pulmonary contusion.
- Metabolic: Lipoid pneumonia.
- Circulatory: Chronic pulmonary venous congestion.
- Idiopathic: Idiopathic pulmonary fibrosis (IPF) in early stages.
Pathophysiology
The crazy paving sign reflects:
- Ground-glass opacity due to alveolar filling (e.g., fluid, protein, cells) or interstitial thickening.
- Thickening of interlobular and intralobular septa caused by edema, fibrosis, or cellular infiltration.
- The combination of these processes produces the characteristic reticulogranular pattern.
Histopathology
- Alveolar filling processes (e.g., proteinaceous material in PAP).
- Interstitial thickening due to edema, inflammation, or fibrosis.
Imaging
Applied Anatomy
- Parts: Involves alveoli and interstitium within secondary pulmonary lobules.
- Size: Variable extent, depending on the underlying condition.
- Shape: Polygonal or mosaic pattern of intersecting lines.
- Position: Diffuse or focal, often bilateral but can be asymmetric.
- Character: Ground-glass opacity with superimposed thickened septa.
- Time: Can be acute, subacute, or chronic, depending on etiology.
CXR
- May demonstrate diffuse or patchy hazy opacities.
- Subtle reticulonodular patterns may occasionally be visible.
- Often non-specific and less sensitive compared to CT.
CT
- Key Modality:
- Ground-glass opacity (GGO) with superimposed interlobular and intralobular septal thickening.
- The pattern is polygonal, resembling irregular stone paving.
- Distribution can be diffuse, patchy, or focal depending on the underlying cause.
- In pulmonary alveolar proteinosis (PAP):
- Bilateral, symmetric involvement, typically in the mid to lower lung zones.
- In Pneumocystis jirovecii pneumonia (PJP):
- Diffuse, bilateral crazy paving pattern with a predilection for perihilar regions.
- Contrast-enhanced CT may help assess associated vascular changes or superimposed complications.
MRI
- Rarely used but may show hyperintense signals corresponding to GGO on T2-weighted imaging.
PET-CT
- Variable metabolic activity depending on the etiology:
- Increased uptake in active infections, malignancies, or inflammation.
- Lower activity in pulmonary alveolar proteinosis.
Other
- Not applicable.
Differential Diagnosis
- Pulmonary alveolar proteinosis (PAP): Classic and most common association.
- Pneumocystis jirovecii pneumonia (PJP): Diffuse, bilateral GGO with crazy paving.
- Organizing pneumonia: Patchy consolidation with ground-glass opacity.
- Pulmonary edema: Septal thickening secondary to fluid accumulation.
- Lipoid pneumonia: Fatty alveolar material causing ground-glass opacity.
- Diffuse alveolar hemorrhage (DAH): Alveolar filling with associated septal thickening.
- NSIP: Reticular pattern with ground-glass opacity.
Recommendations
- Further Imaging:
- Contrast-enhanced chest CT to assess underlying vascular, neoplastic, or inflammatory processes.
- Prone imaging may help differentiate dependent atelectasis from true disease involvement.
- Laboratory Correlation:
- Bronchoalveolar lavage (BAL) for infectious or proteinaceous causes.
- Serum markers for inflammatory or autoimmune etiologies (e.g., ACE, ANA).
- Fungal and viral serology in infectious conditions.
- Biopsy: Consider transbronchial or surgical lung biopsy in uncertain cases.
Key Points and Pearls
- The crazy paving sign is not disease-specific but strongly associated with pulmonary alveolar proteinosis (PAP).
- Careful evaluation of distribution, associated findings, and clinical context is key to narrowing the differential diagnosis.
- A combination of alveolar and interstitial processes produces the characteristic radiologic pattern.
- Infectious causes, particularly PJP, are important considerations in immunocompromised patients.
- characterized by
- scattered or diffuse
- ground-glass attenuation with
- superimposed interlobular septal thickening and
- intralobular lines
Diagram shows inflammation (red ) in the walls of the alveoli with thickening of the interlobular septa (maroon) . The increased density in the interalveolar septa and interlobular septa results in a ground glass opacity with and crazy paving appearance on CT scan
Ashley Davidoff TheCommonVein.net
lungs-0736a
Ashley Davidoff TheCommonVein.net ARDS-crazy-paving
- Causes
- Infection
- Pneumocystis carinii pneumonia
- severely immunocompromised patient
- Pneumocystis carinii pneumonia
- Inflammatory
- Sarcoidosis
- NSIP
- Organizing Pneumonia
- Neoplasm
- Mucinous bronchioloalveolar carcinoma
- Circulatory
- Hemorrhage
- Idiopathic
- Alveolar proteinosis
- Inhalational
- Lipoid pneumonia
- Systemic Disease
- Infection
The Secondary Lobule
Keywords:
lung pulmonary alveoli alveolus secondary lobule interlobular septa vein lymphatic histology interstitium interstitial normal
Courtesy of: Armando Fraire, M.D. Ashley Davidoff TheCommonVein.net
Thickened Interlobular Septa due to Inflammation – Acute Eosinophilic Pneumonia
The diagram shows the thickened septum surrounding the secondary lobule due to an inflammatory process, cellular infiltrate and congestion of the venules and lymphatics in the septum (a) . An anatomic specimen of a secondary lobule from a patient with thickened interlobular septa is shown in c and overlaid in d. CT of the lungs in a patient with acute eosinophillic pneumonia shows thickened interlobular septa and centrilobular nodules and the thickened septa are overlaid in red (e).
Ashley Davidoff MD The CommonVein.net
lungs-0761
Anthracosis – Note the accumulation of carbon particles within the lymphatics along the interlobular septa, outlining the secondary lobules. The carbon particles are inhaled from an anthracotic urban environment. Courtesy Ashley Davidoff MD. TheCommonVein.net 32291 key words lung interlobular septum septa secondary lobule pulmonary lobule intertstitium interstitial gross pathology carbon
Infection
Rossi, S.E et al “Crazy-Paving” Pattern at Thin-Section CT of the Lungs: RadiologicPathologic Overview Radiographics Volume 23 – Number 6, 2003
Inflammatory Diseases
ARDS
Ashley Davidoff
TheCommonVein.net
Ashley Davidoff
TheCommonVein.net
77F with Aspiration Pneumonia ARDS and Crazy Paving
- Inflammation
- Sarcoidosis
Sarcoidosis in a 25-year-old asymptomatic
man. High-resolution CT scan shows scattered bilateral
areas of ground-glass attenuation associated with inter and intralobular lines.
Rossi, S.E et al “Crazy-Paving” Pattern at Thin-Section CT of the Lungs: RadiologicPathologic Overview Radiographics Volume 23 – Number 6, 2003Amyloidosis
Diffuse alveolar-septal amyloidosis
CT scan in the axial projection at the base of the lungs show many features of amyloidosis including lung nodules (white arrowheads) and infiltrates (b), and diffuse deposition within the alveolar septa (red arrowheads, c) and centrilobular nodules(yellow arrow c)
Ashley Davidoff MD Boston Medical Center
TheCommonVein.net septal-amyloidosis-001bNSIP
-
Methotrexate-induced NSIP in a 41-year-old woman with rheumatoid arthritis who presented with dyspnea and decreased diffusing capacity of the lungs for carbon monoxide (Dlco). (a) High-resolution CT scan shows
scattered ground-glass attenuation and thickened inter- and intralobular lines (arrow). (b) Photomicrograph (original
magnification, 400; hematoxylin-eosin stain) of a specimen from lung biopsy shows patchy interstitial fibrosis, expansion of the interstitium by chronic inflammatory infiltrates, and reactive hyperplastic type II pneumonocytes (arrow), findings consistent with NSIP induced by the pulmonary toxic effects of methotrexate.
Diffuse mucinous bronchioloalveolar carcinoma in a 78-year-old man. (a) High-resolution CT scan
shows a bilateral crazy-paving pattern and centrilobular nodules. (b) Photomicrograph (original magnification,
400; hematoxylin-eosin stain) of a specimen from open lung biopsy shows replacement of the alveolar epithelium
by epithelial neoplastic cells with abundant intracytoplasmic mucin (arrows).
Rossi, S.E et al “Crazy-Paving” Pattern at Thin-Section CT of the Lungs: RadiologicPathologic Overview Radiographics Volume 23 – Number 6, 2003
- Sarcoidosis
- Neoplasm
Diffuse mucinous bronchioloalveolar carcinoma in a 78-year-old man. (a) High-resolution CT scan
shows a bilateral crazy-paving pattern and centrilobular nodules. (b) Photomicrograph (original magnification,
400; hematoxylin-eosin stain) of a specimen from open lung biopsy shows replacement of the alveolar epithelium
by epithelial neoplastic cells with abundant intracytoplasmic mucin (arrows).
Rossi, S.E et al “Crazy-Paving” Pattern at Thin-Section CT of the Lungs: RadiologicPathologic Overview Radiographics Volume 23 – Number 6, 2003Primary lung adenocarcinoma in a 54-year-old man with hemoptysis. (a) Posteroanterior chest radiograph shows a centrally located mass adjacent to an area of diffuse ground-glass opacity in the right upper lobe. Note
the air trapping in the lung base. (b) CT scan shows typical crazy-paving ground-glass attenuation associated with
septal thickening surrounding the mass, which is perihilar. Adenocarcinoma with surrounding pulmonary hemorrhage was confirmed at surgery
Rossi, S.E et al “Crazy-Paving” Pattern at Thin-Section CT of the Lungs: RadiologicPathologic Overview Radiographics Volume 23 – Number 6, 2003 - Circulatory Disorders
- Hemorrhage
-
Acute diffuse pulmonary hemorrhage in a 53-year-old woman with systemic lupus erythematosus and
massive hemoptysis. (a) High-resolution CT scan shows geographic areas of ground-glass attenuation with interlobular septal thickening. (b) Photomicrograph (original magnification, 250; hematoxylin-eosin stain) shows acute intraalveolar hemorrhage.
Rossi, S.E et al “Crazy-Paving” Pattern at Thin-Section CT of the Lungs: RadiologicPathologic Overview Radiographics Volume 23 – Number 6, 2003 - CHF Rare
-
CHF and Crazy Paving
44-year-old man with dyspnea and cough diagnosed as having congestive heart failure. CT of the thorax shows diffuse, multifocal, patchy, ground-glass opacities (arrow).
Şentürk A, et al A Rare Cause of Crazy-Paving and Mediastinal Lymphadenopathy: Congestive Heart Failure Journal of Clinical Imaging Science 3(1):30 July 2013
-
Idiopathic
- Alveolar Proteinosis
Alveolar proteinosis in a 37-year-old woman with a nonproductive cough and dyspnea. (a) Posteroanterior chest radiograph shows bilateral reticular areas of increased opacity, which occur predominantly in the lower
zones. (b) High-resolution CT scan shows diffuse geographic ground-glass attenuation with superimposed intra- and
interlobular septal thickening (arrowhead). Note the polygonal appearance, which represents the secondary pulmonary lobule. (c, d) Photomicrographs (original magnification, 400; hematoxylin-eosin [c] and periodic acid–Schiff
[d] stains) of a specimen from transbronchial biopsy show alveolar spaces filled by a dense, eosinophilic, granular
proteinaceous material () that is positive for periodic acid–Schiff stain.
Rossi, S.E et al “Crazy-Paving” Pattern at Thin-Section CT of the Lungs: RadiologicPathologic Overview Radiographics Volume 23 – Number 6, 2003
-
Inhalational
- Lipoid pneumonia
-
Lipoid pneumonia in a 64-year-old woman with a 20-year history of scleroderma who presented with progressive dyspnea and a dry cough. (a) Posteroanterior chest radiograph shows bilateral, asymmetric, scattered areas of increased opacity in the air space, which have a predominantly perihilar and basal distribution. (b) High-resolution CT scan shows geographic ground-glass attenuation in association with interlobular thickening and intralobular lines (arrow). The results of bronchoalveolar lavage and transbronchial biopsy were nondiagnostic. (c) Photomicrograph (original magnification, 250; hematoxylin-eosin stain) of a specimen from open lung biopsy shows numerous lipid-laden macrophages that fill and distend the alveoli (arrow) and interstitium.
Rossi, S.E et al “Crazy-Paving” Pattern at Thin-Section CT of the Lungs: RadiologicPathologic Overview Radiographics Volume 23 – Number 6, 2003
-
Systemic Disease
CT scan shows Diffuse ground glass pattern with thickening of the interlobular septa and manifesting as crazy paving pattern
Ashley Davidoff MD
Source
Signs in Thoracic Imaging
Journal of Thoracic Imaging 21(1):76-90, March 2006.
Crazy paving in ILD is a CT feature of interstitial lung disease and is characterised by diffuse ground glass caused by a combination of interlobular septal and intralobular septal thickening resulting well demarcated patchy densities in the lungs.
Idiopathic
57-year-old female with progressive dyspnea.
Ashley Davidoff MD
Ashley Davidoff MD
Ashley Davidoff MD
Ashley Davidoff MD
Ashley Davidoff MD
Ashley Davidoff MD
Ashley Davidoff MD
Ashley Davidoff MD
References and Links
- Rossi, S.E et al “Crazy-Paving” Pattern at Thin-Section CT of
the Lungs: RadiologicPathologic Overview Radiographics Volume 23 – Number 6, 2003 - TCV